This application claims the benefit of Korean Patent Application No. P00-32588, filed on Jun. 14, 2000, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly, to a transparent reflective liquid crystal display that is capable of improving a light efficiency and a color purity.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT""s) as switching devices to display a natural moving picture. Since such a liquid crystal display can be made into a smaller-size device than a CRT (cathode ray tube), it is commercially available as a monitor in portable devices, such as portable televisions, laptop personal computers, and the like.
Such a LCD requires a separate light source because it is not a self-emitting device. The LCD can be largely classified into a transmissive type and a reflective type depending on a type of light source. The transmissive LCD has a backlight unit installed opposite the rear substrate of two transparent substrates into which a liquid crystal is injected, to transmit light being input from the backlight unit to a screen. On the other hand, the reflective LCD has a reflective surface formed on the rear substrate of two transparent substrates into which a liquid crystal is injected, to reflect an external light or a separate auxiliary light incident the rear substrate via the front substrate to a screen.
Recent investigations have been made to study a transparent reflective LCD capable of having the advantages of both the transmissive type and the reflective type.
Referring to FIG. 1, the conventional transparent reflective LCD includes a front substrate 108 and a rear substrate 104 having a liquid crystal 106 injected therebetween, a xcex/4 plate 109 and a linear polarizer 110 disposed on the front surface of the front substrate 108, an absorptive color filter 107 installed between the front substrate 108 and the liquid crystal 106, a xcex/4 plate 103 and a linear polarizer 102 disposed on the rear surface of the rear substrate 104, and a metal reflecting plate 105 installed between the rear substrate 104 and the liquid crystal 106. Holes 105a are defined in the metal reflecting plate 105 at a desired interval.
An external light is converted into a specific linear-polarized light by means of the linear polarizer 110 and thereafter is converted into a circular-polarized light by means of the xcex/4 plate 109 to be incident to the metal reflecting plate 105 via the absorptive color filter 107 and the liquid crystal 106. The external light being incident to the metal reflecting plate 105 retrogresses a light path to go toward the display screen. At this time, the absorptive color filter 107 transmits only a visible light having a specific wavelength band and absorbs a light beam having other wavelength bands. A light input from the backlight unit 101 is converted into a specific linear-polarized light by means of the linear polarizer 102, is then converted into a circular-polarized light by means of the xcex/4 plate 103 to traverse the rear substrate 104, and thereafter is incident to the metal reflecting plate 105. Light from the backlight unit 101 incident the metal reflecting plate 105 in this manner also is incident the liquid crystal 106 via a hole 105a of the metal reflecting plate 105, and then goes toward the display screen via the liquid crystal 106.
However, the conventional transparent reflective LCD has a drawback in that a light irradiated from the backlight unit 101 has a large light loss due to the linear polarizer 102 at the rear substrate side. Consequently, a light absorption ratio of the linear polarizer 102 is about 55% or more. Also, only a portion of the light passing through the linear polarizer 102 goes toward the display screen via the hole 105a of the metal reflecting plate 105. At this time, since light reflects from the metal reflecting plate 105 without passing through the hole 105a and retrogresses a light path incident to the linear polarizer 102 in a changed polarization state, most reflective light is absorbed by the linear polarizer 102. In the case of displaying a picture or an image using the transmissive type, a light efficiency is deteriorated because only a slight portion of a light generated from the backlight unit 101 is utilized for a display light. Furthermore, the conventional transparent reflective LCD has a problem in that it is difficult to obtain acceptable color purity.
Accordingly, the present invention is directed to a transparent reflective liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
In one aspect of the present invention, a transparent reflective liquid crystal display is provided with a structure adapted for improving light efficiency.
In another aspect of the present invention, a transparent reflective liquid crystal display is provided with a structure that provides adequate color purity.
In order to achieve these and other objects of the invention, a transparent reflective liquid crystal display device according to an embodiment of the present invention includes a first circular polarizer for transmitting a circular-polarized light input from a backlight unit having a first direction while reflecting a circular-polarized light having a second direction contrary to the first direction. A second circular polarizer is arranged in opposition to the first circular polarizer and transmits circular-polarized light having the second direction while reflecting the circular-polarized light having the first direction. Such an arrangement that includes a pair circular polarizers can improve the ratio of light reaching a display screen from a backlight unit to the light emitted from a backlight unit.
To provide increased color purity, a circular-polarizing color filter is provided at one side of the second circular polarizer for extracting a circular-polarized light having a specific visible light wavelength band in the circular-polarized light having the first direction, and a reflecting member is arranged in opposition to the second circular polarizer to reflect light from an external source. The reflecting member has a hole formed in opposition to the circular-polarizing color filter to transmit the circular-polarized light having the specific visible light wavelength band via the hole.
A transparent reflective liquid crystal display device according to another embodiment of the present invention includes a circular polarizer for transmitting a circular-polarized light having a first direction input from the backlight unit while reflecting a circular-polarized light having a second direction contrary to the first direction. A xcex/4 plate is arranged in opposition to the circular polarizer for converting a circular-polarized light input from the circular polarizer into a linear-polarized light having a specific direction.
To improve color purity, a first circular-polarizing color filter is provided for reflecting a circular-polarized light having a specific visible light wavelength band in a circular-polarized light from an external light source, and a light-absorbing member is provided at a rear side of the circular-polarizing color filter for absorbing light that transmits through the circular-polarizing color filter. Between the first xcex/4 plate and the light-absorbing member, a reflecting member may be provided for reflecting light, and a second circular-polarizing color filter for transmitting a circular-polarized light having a specific visible light band in the circular-polarized light input from the circular polarizer may be provided in a hole passing through the first circular-polarizing color filter, the light-absorbing member, the reflecting member, and/or the xcex/4 plate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention, as claimed.